Low temperature air fractionation system

ABSTRACT

The invention relates to a low temperature air fractionation system comprising several modules consisting of at least one heat exchange unit, a pressure column and a low pressure column, in addition to the accessories belonging to the respective modules and at least two cold-boxes, wherein the module and/or the accessories are arranged. The invention is characterised in that at least one of the cold-boxes is embodied in the form of a main box and at least one of the cold-boxes is embodied in the form of a secondary box. The secondary box contains at least one module and the accessories of the module disposed in the secondary box are mainly located in the main box.

[0001] The invention relates to a low-temperature air separation systemwith several modules, which comprise at least one heat exchanger unit, apressure column, and a low-pressure column, and with the accessoriesthat belong to the respective modules and with at least two coldboxes,in which the modules and/or the accessories are located.

[0002] To recover argon by low-temperature rectification, a fractioncontaining essentially oxygen, nitrogen and argon is removed from thelow-pressure column of a two-column apparatus at an intermediate siteand delivered to a raw argon column. Then, oxygen is removed from theargon in the raw argon column, and the argon is removed at the head ofthe raw argon column as an oxygen-free product. The raw argon column isordinarily located such that its bottom is located roughly at the heightof the argon taphole of the low-pressure column.

[0003] Under certain circumstances, the raw argon column, however, has avery large structural height so that the set-up and alignment of the rawargon column and the thermal insulating jacket that surrounds thecolumn, a so-called coldbox, become very complex. In EP-A-0 628 777, itis therefore proposed that the raw argon column be divided into twocomponent columns, the first component column extending from the heightof the argon taphole to at most the head of the low-pressure column andthe size of the second component column being chosen according toprocess conditions.

[0004] EP-A-0 870 524 uses this approach and suggests a low-temperatureair separation system in which the raw argon column is likewise dividedand the columns are arranged such that the coldbox surrounding thecolumns is filled as completely as possible.

[0005] Larger low-temperature air separation systems of this type are,however, not transportable and must therefore be set up where they areto be used. Even when the system is divided into a rectification module,in which essentially oxygen-nitrogen separation takes place, and into anargon module that comprises a raw argon column with its accessories, thetwo coldboxes are often so large that they are no longer transportable.Production at the manufacturer's plant is thus not possible.

[0006] The object of this invention is to develop a low-temperature airseparation system that is as easy as possible to produce.

[0007] This object is achieved according to the invention by a system ofthe initially mentioned type in which at least one of the coldboxes ismade as the main box and at least one of the coldboxes is made as asecondary box, the secondary box containing at least one of the modulesand the accessories of the module that is located in the secondary boxbeing located primarily in the main box.

[0008] Within the framework of this description, the components of thelow-temperature air separation system are conceptually divided intomodules, accessories and piping. The modules comprise all componentsthat enable one of the functions specific to low-temperature airseparation. The modules that are to be thermally insulated includeespecially machines such as, e.g., expansion machines and cryogenicpumps, heat exchange devices, such as, e.g., the main heat exchanger,main condenser, head condensers and secondary condensers, as well asequipment for separation of air, such as countercurrent heat exchangersand rectification columns.

[0009] Among the accessories are especially the instrumentation,fittings, measuring devices, e.g., for flow rate measurements andanalysis, measurement lines and inspection means and similar structuraldevices. The pipelines are not included among the accessories within theframework of this description, if not indicated explicitly otherwise,but are considered separately.

[0010] A coldbox is defined as a container, a jacket or a covering thatis suitable for accommodating one or more components, especiallymodules, of a low-temperature air separation system and insulating themthermally against the environment. The coldbox is either itselfthermally insulated or can be filled with a suitable thermal insulationmaterial.

[0011] According to the invention, the modules to be housed in thecoldboxes, i.e. the modules that are to be thermally insulated, aredivided among at least two coldboxes. For example, the two componentcolumns of a divided raw argon column each can have its own coldbox. Thepressure column and the low-pressure column can be accommodated inanother coldbox or likewise divided among two coldboxes. In this way,the coldbox sizes can be reduced, facilitating transport.

[0012] The division of the modules among the coldboxes takes placeaccording to the invention such that at least one coldbox is kept assimple as possible. This is achieved in the sense of the invention byone coldbox being made as a secondary box in which essentially onlymodules without their accessories are located. A main box is assigned tothe secondary box and contains most of the accessories of the moduleslocated in the secondary box. The secondary box can thus be made verysimple and is easy and economical to produce.

[0013] The main box is preferably made such that it comprises not onlythe accessories of the assigned secondary box, but itself contains oneof the modules. Under certain circumstances it is also a good idea toaccommodate only the accessories of the modules of the secondary boxesin the main box.

[0014] The invention is especially valuable in a low-temperature airseparation system that has a raw argon rectification unit that comprisesa first and a second component column, a raw argon line that leads fromthe upper area of the first component column into the lower area of thesecond component column, means for returning the reflux liquid from thebottom of the second component column to the upper area of the firstcomponent column and an argon head condenser with a condensation sidethat is connected to the upper area of the second component column.

[0015] The raw argon column in one such system is divided into two partsin order to reduce the structural height. The two component columns arehoused in different coldboxes. The first component column itself doesnot have a head condenser, but is supplied from the bottom of the secondcomponent column with the necessary reflux liquid. The first componentcolumn therefore has essentially only connections for delivering anddischarging liquid and gas to the low-pressure column and to the secondcomponent column.

[0016] Preferably the accessories to the first component column, suchas, e.g., the inspection devices, measurement and analysis means, arenot located in the coldbox that contains the first component column, butmainly in the coldbox for the second component column. The coldbox withthe first component column can thus be made very simple and in the senseof this invention constitutes the secondary box. The second coldboxcontains as the main box the second component column, the argon headcondenser and the accessories to the two component columns. The rawargon rectification unit can thus be divided into two modules, andneither exceed allowable transport dimensions, and the first module canbe prefabricated especially easily.

[0017] In one especially preferred version, a pure argon column with itsaccessories is integrated into the main box with the second componentcolumn. Not only all accessories, but also all the piping of the rawargon rectification unit are especially preferably located in the mainbox.

[0018] In addition to the described division of the raw argonrectification unit into a secondary box with the first component columnand a main box with the second component column, a division of the rawargon rectification unit into a main box with two assigned secondaryboxes has proven advantageous, especially in very large air separationsystems.

[0019] In this variant, the raw argon rectification unit is likewisedivided into two component columns. Preferably the two component columnsare each located in a secondary box. In this case, a first secondary boxencompasses the first component column, and a second secondary boxencompasses the second component column with the argon head condenser.For the accessories of the two component modules, there is a main boxthat also contains especially preferably the piping of the two componentcolumns.

[0020] If the argon rectification unit is provided with a pure argoncolumn, it is advantageous to place the pure argon column with theaccessories in the main box.

[0021] Preferably more than 60%, especially preferably more than 70% andquite especially preferably more than 80% of accessories of the modulesof the secondary box are housed in the pertinent main box. In otherwords, in the secondary box are at most 40% of the fittings, at most 40%of the instruments, at most 40% of the measurement lines and means andat most 40% of the inspection means. Preferably the portion of theabove-mentioned accessories located in the secondary box is at most 30%,especially preferably at most 20%.

[0022] The piping of the module housed in the secondary box is quiteespecially preferably located mostly in the assigned main box,advantageously more than 60%, especially advantageously more than 70%and quite especially advantageously more than 80% of the piping beingassigned to the main box.

[0023] For production reasons, it is a good idea to make the main boxand the secondary box cuboidal, i.e., with a rectangular outline, sincein this way the connections to the boxes and the lines through the wallsof the boxes are easier to produce. It also yields advantages, however,when the shape of the main box and/or of the secondary box is matched tothe shape of the modules and/or accessories that are to be housed in thebox. Thus, it is advantageous to surround a rectification column that isto be housed in the secondary box, for example the first componentcolumn of a divided raw argon rectification unit, with a cylindricalbox.

[0024] The concept of division into a main box with an assignedsecondary box according to the invention that has proven itself in adivided raw argon column can, of course, also be applied to thenitrogen-oxygen rectification unit. It is likewise advantageous to placethe pressure column and the low-pressure column in one secondary boxeach and to provide a main box that contains essentially only theaccessories of the pressure column and low-pressure column. Furthermore,a version in which in the main box is the low-pressure column,optionally with a supercooling countercurrent heat exchanger, and in thesecondary box is the pressure column, preferably with the maincondenser, is advantageous. The variant in which the coldbox of thepressure column is made as the main box and that of the low-pressurecolumn is made as the secondary box also yields advantages. In all ofthe above-mentioned variants, there is preferably a large part of thepiping in the main box.

[0025] The invention and further details of the invention are explainedbelow using embodiments shown in the schematics. Here:

[0026]FIG. 1 shows the process diagram of an air separation systemaccording to the invention,

[0027]FIGS. 2a and 2 b show air separation systems according to theinvention in which a divided raw argon column is housed in a main boxand a secondary box,

[0028]FIGS. 3a and 3 b show an alternative division of a divided rawargon column among the main and secondary boxes, and

[0029] FIGS. 4 to 6 show analogous versions with division of thepressure and low-pressure column among the main and secondary boxes.

[0030] The air separation system shown in FIG. 1 has a double columnrectifier with a main condenser 1, a pressure column 2, and alow-pressure column 3 for recovering nitrogen at the head of thelow-pressure column 3 and oxygen from the bottom of the low-pressurecolumn 3. The double column is housed jointly with the supercoolingcountercurrent heat exchanger 4 and other cold components that are notshown, such as, e.g., cryogenic pumps, housed in several coldboxes thatare arranged as explained in more detail using FIGS. 2 to 6.

[0031] The argon rectification unit consists of two component columns 6,7 that form a raw argon column, of a pure argon column 8 and thecorresponding head condensers 9, 10. The first component column 6 isconnected to the low-pressure column 3 in the conventional manner by aline 17, via which a fraction containing essentially oxygen and argoncan be fed into the first component column 6. The return line 18 is usedto return residual liquid that collects in the bottom of the firstcomponent column 6 to the low-pressure column 3. In this return line 18,there is a pump 12 for delivering the residual liquid.

[0032] The first component column 6 does not have a head condenser. Thereflux liquid for this column 6 is formed by the bottom liquid of thesecond component column 7 that is pumped by means of a pump 11 to thehead of the component column 6. In the head condenser 9, the refluxliquid for the second part 7 of the raw argon column is produced bycondensation of the head fraction in indirect heat exchange with thebottom liquid from the pressure column 2 that is supplied via the line19. The resulting vapor is returned to the low-pressure column 3 via theline 13. Excess bottom liquid is supplied to the low-pressure column 3from the head condenser 9 via the line 14. Analogously, the headcondenser 10 of the pure argon column 8 is supplied with bottom liquidfrom the pressure column 2. The vapor that forms and the excess liquidare routed likewise into the low-pressure column 3 via the lines 15 and16 that discharge into the lines 13 and 14.

[0033] All parts of the system that are to be thermally insulated arehoused in coldboxes that are filled with perlite. The division of theindividual models and accessories is explained in more detail belowusing FIGS. 2 to 6. In drawings 2 to 6, the main box is outlined with athick line, the secondary box is shown by the broken line, and theassignment of the main and secondary box is illustrated by a doublearrow. The rectangle symbolizes respectively the coldbox 21 for the mainheat exchanger 5. Squares and rectangles drawn with an ordinary linethickness identify conventional coldboxes without the main or secondarybox character according to the invention.

[0034] In the arrangement according to FIG. 2, the main heat exchanger5, the pressure column 2, the low-pressure column 3, and the twocomponent columns 6, 7 for raw argon rectification are each housed inits own coldbox 21, 22, 23, 24, 25. The coldbox 25 that contains thesecond component column 7 is made as the main box to which the coldbox24 that contains the first component column 6 is assigned as thesecondary box. The main box 25 comprises in addition to the componentcolumn 7 also the argon head condenser 9, the pure argon column 8 andits head condenser 10. Furthermore, more than three fourths of theaccessories of the first component column 6, i.e. the measurement andcontrol means, the fittings and the inspection means as well as morethan three-fourths of the piping of the first component column arelocated in the main box 25.

[0035]FIG. 2b shows an alternative embodiment in which there is a commoncoldbox 26 for the pressure column 2 and the low-pressure column 3. Thecoldboxes 24, 25 of the two component columns 6 and 7 likewise have themain box-secondary box ratio explained using FIG. 2a.

[0036] The individual coldboxes are interconnected among one another viaconnecting boxes in which, for example, the connecting lines run. It isalso advantageous for all the arrangements shown in the Figures to placedirectly next to one another two or more coldboxes that must beconnected to one another, to connect them to one another and to removethe common wall of the coldboxes so that a single coldbox is formed.

[0037] The two embodiments according to FIG. 3a and FIG. 3b differ fromthose of FIGS. 2a and 2 b in that the second component column 7 islikewise located in a secondary box 27. The main box 28 comprises mostof the accessories of the two component columns 6, 7, the pure argoncolumn 8 and the condensers 9, 10 and the pure argon column 8.Furthermore, the cold piping of the two raw argon component modules 6,7, i.e. the piping to be insulated, is contained in the main box 28. Thepressure column 2 and the low-pressure column 3 are each housed in itsown coldbox 22, 23.

[0038]FIG. 3b corresponds essentially to FIG. 3a, however the pressurecolumn 2 and the low-pressure column 2, analogously to the executionaccording to FIG. 2b, are located in a common coldbox 26. The argonrectification unit with the two component columns 6, 7 is divided amongtwo secondary boxes 24, 27 for the component columns 6, 7 and a main box28 that contains the corresponding accessories and the piping.

[0039] FIGS. 4 to 6 show other embodiments of the concept according tothe invention in the division of the coldboxes into main and secondaryboxes.

[0040]FIG. 4a shows a low-temperature air separation system in which thecoldbox for the double column consisting of the pressure column 2 andthe low-pressure column 3 is divided according to the invention. In thiscase, the low-pressure column 3 is housed in a secondary box 35. Thepressure column 2 with the main condenser and the accessories of thelow-pressure column 3 is located in the main box 34. The raw argoncolumn is divided and, as already shown in FIG. 2, is likewise locatedin two coldboxes 24, 25 that are made as the main and secondary box. Forlarge systems, this version itself allows the transport of individualmodules with the pertinent coldboxes.

[0041]FIG. 4b shows one modification of the arrangement of FIG. 4a, inwhich the raw argon column is divided and is housed in two coldboxes 31,32, in which the two coldboxes 31, 32 for the first and the secondcomponent column 6, 7 are made in the conventional manner, i.e., inwhich all of the accessories assigned to the respective componentcolumns 6, 7 are also located in the corresponding coldbox 31, 32.

[0042] In another variant 4 c of this embodiment that is preferredespecially in a system with a smaller argon rectification unit, there isa common coldbox 33 for the two component columns 6, 7 for argonrecovery. The two component columns 6, 7 are generally located next toone another. It has also proven advantageous, however, to provide thesecond component column 7 with the head condenser under the firstcomponent column 6. Since the bottom of the first component column 6 islocated at the height of the argon tap from the low-pressure column 3,in the coldbox 33 underneath the first component column 6 there is spacethat is used preferably for the second component column 7. To supply thefirst component column 6 with reflux liquid, bottom liquid from thesecond component column 7 is pumped to the head of the first componentcolumn 6.

[0043] Instead of the embodiment of the pressure column box as the mainbox and the low-pressure column box as the secondary box, it can also beadvantageous to embody vice versa the pressure column box 29 as thesecondary box and the low-pressure column box 30 as the main box.Various variants of this embodiment are shown in FIGS. 5a to 5 c. FIGS.5a to 5 c correspond here to the arrangements according to FIGS. 4a to 4c, only the main box-secondary box relation between the pressure columnbox and the low-pressure column box being interchanged. The maincondenser can be located either with the low-pressure column 3 and theaccessories of the pressure column 2 and those of the low-pressurecolumn 3 in the main box 30 or placed preferably on or above thepressure column 2 and installed in the secondary box 29.

[0044]FIGS. 6a to 6 d shows other advantageous variants. According toFIG. 6a, there is a separate main box 36 for the accessories of thepressure column 2 and the low-pressure column 3. The pressure column 2and the low-pressure column 3 are conversely each housed in a secondarybox 29, 35. This has the advantage that the two secondary boxes 29, 35can be produced more easily since they contain essentially only therespective rectification column 2, 3. In a preferred embodiment, themain condenser is also integrated here into the secondary box 29 withthe pressure column. The two component columns 6, 7 of the raw argoncolumn are likewise interconnected in two via the main box-secondary boxprinciple according to the invention.

[0045]FIGS. 6b and 6 c show slight modifications of the arrangementaccording to FIG. 6a, in which the two component columns 6, 7 arehoused, on the one hand, in two conventional coldboxes 31, 32 that arenot connected to one another according to the invention (FIG. 6b), and,on the other hand, can be found in a common coldbox 33 (FIG. 6c).Finally, FIG. 6d shows an arrangement in which both the pressure column2 and the low-pressure column 3 as well as the two component columns 6,7 are housed in separate secondary boxes 29, 35, 24, 27, and there aretwo main boxes 36, 28 that are assigned, on the one hand, to thesecondary boxes 29, 35, and, on the other hand, to the secondary boxes24, 27. An arrangement in which a single main box is connected to thefour secondary boxes 29, 35, 24, 27 is not shown, but is alsoadvantageous depending on the number and size of the accessories.

[0046] The various figures are intended to illustrate the type ofcoldboxes used for the different modules, i.e., whether a main box, asecondary box, or a conventional coldbox is used. Their arrangement toone another is not absolutely correctly reproduced in the figures.Preferably, the coldboxes are arranged such that the coldboxes betweenwhich many pipe connections and other connecting lines run are as closetogether as possible. Thus, for example, it is advantageous to locatethe coldbox 21 with the main heat exchanger next to the low-pressurecolumn box and to have the pressure column box and the raw argon columnbox(es) border the low-pressure column box. The connection of thecoldboxes among one another takes place via insulated connecting boxesor by joining the affected coldboxes to one another and removing theintermediate wall.

1. Low-temperature air separation system with several modules that comprise at least one heat exchanger unit, a pressure column, and a low-pressure column, and with the accessories that belong to the respective modules and with at least two coldboxes in which the modules and/or the accessories are located, characterized in that at least one of the coldboxes is made as the main box (25, 28, 30, 34, 36) and at least one of the coldboxes is made as a secondary box (24, 27, 29, 35), the secondary box (24, 27, 29, 35) containing at least one of the modules (2, 3, 6, 7) and the accessories of the module (2, 3, 6, 7) that is located in the secondary box (24, 27, 29, 35) being located primarily in the main box (25, 28, 30, 34, 36).
 2. Low-temperature air separation system according to claim 1, wherein there is at least one module (2, 3, 7) in the main box (25, 30, 34).
 3. Low-temperature air separation system according to claim 1, wherein there are no modules in the main box (28, 36).
 4. Low-temperature air separation system according to one of claims 1 to 3, wherein there is a raw argon rectification unit that comprises a first and a second component column (6, 7), a raw argon line that leads from the upper area of the first component column (6) into the lower area of the second component column (7), means (11) for returning the reflux liquid from the bottom of the second component column (7) to the upper area of the first component column (6) and an argon head condenser (9) with a condensation side that is connected to the upper area of the second component column (7), the secondary box (24) containing the first component column (6) and the main box (25) containing the second component column (7) and the argon head condenser (9) and most of the accessories of the first component column (6).
 5. Low-temperature air separation system according to claim 4, wherein the main box (25) contains a pure argon column (8).
 6. Low-temperature air separation system according to one of claims 1 to 3, wherein there is a raw argon rectification unit that comprises a first and a second component column (6, 7), a raw argon line that leads from the upper area of the first component column (6) into the lower area of the second component column (7), means (11) for returning the reflux liquid from the bottom of the second component column (7) to the upper area of the first component column (6) and an argon head condenser (9) with a condensation side that is connected to the upper area of the second component column (7), the main box (28) containing most of the accessories of the raw argon rectification unit and the first component column (6) being housed in a first secondary box (24) and the second component column (7) and the argon head condenser (9) being housed in a second secondary box (27).
 7. Low-temperature air separation system according to claim 6, wherein the second secondary box (27) contains a pure argon column (8).
 8. Low-temperature air separation system according to one of claims 1 to 7, wherein more than 60%, preferably more than 70%, especially preferably more than 80% of accessories are located in the main box (25, 28, 30, 34, 36).
 9. Low-temperature air separation system according to one of claims 1 to 8, wherein the pressure column (2) and the low-pressure column (3) are each located in a secondary box (29, 35), and the main box (36) contains essentially only the accessories of the pressure column (2) and of the low-pressure column (3).
 10. Low-temperature air separation system according to one of claims 1 to 8, wherein in the main box (30) is the low-pressure column (3) and in the secondary box (29) is the pressure column (2).
 11. Low-temperature air separation system according to one of claims 1 to 8, wherein in the main box (34) is the pressure column (2) and in the secondary box (35) is the low-pressure column (3).
 12. Low-temperature air separation system according to one of claims 1 to 11, wherein there is a secondary box that contains a raw argon rectification unit.
 13. Low-temperature air separation system according to one of claims 1 to 12, wherein the piping assigned to the module (2, 3, 6, 7) that is located in the secondary box (24, 29, 35) is located primarily in the main box (25, 28, 30, 34, 36). 